How to achieve over 2 TB/hr network backup with Integrity entry-class servers running HP-UX 11i v3

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HP StorageWorks Ultrium 1840 LTO-4 limit testing
For optimal performance with tape devices, the most important contributing factor is providing data
streaming continuously at the maximum throughput capacity of the device. If continuous data
streaming to the tape device is not maintained, the device must stop media movement, reposition the
media, and then restart the media when sufficient data is available to write to the media. These
stop/reposition/restart cycles not only decrease throughput performance but also can cause excessive
media and device wear.
The HP StorageWorks Ultrium 1840 LTO-4 tape device can transfer data at a rate of 240MB/s
(assuming 2:1 compression). The HP LTO-4 drives include HP’s exclusive Data Rate Matching feature,
which further optimizes performance by matching the host system I/O data speed to keep drives
streaming consistently. This enables the tape drives to be one of the fastest in the industry today.
Figure 4 shows results of stress testing performed to identify the maximum I/O throughput rate to one
HP LTO-4 tape drive. The tests use the same data type and mix specified for other tests performed for
the characterization project. The more compressible the data, the higher the I/O throughput rate to
the tape media. With less compressible data, the I/O throughput rate decreases toward the native
speed of the tape device. The HP LTO-4 devices have a native I/O rate of 120 MB/s.
Figure 4: HP StorageWorks Ultrium 1840 LTO-4 tape drive stress test results
The test results in Figure 4 indicate that, given the backup data mix being used for these tests, eight
data streams from clients is optimal to keep a LTO-4 tape drive streaming at maximum speed. More
data streams can be used in parallel to the device, but the overall backup time may actually be longer
if any of the backup tape devices are left unused or only partially used. Configuring more active
parallel data streams than is optimal can also result in longer restore times, as the backup data for
one client is interleaved throughout a longer portion of the backup media.
These results show that the backup utility tuning combination of 8 buffers and 64KB I/O blocks, which
was optimal for the single client 1GbE port in tests reported previously, is not optimal for maintaining
data streaming to an LTO-4 tape device. Because the goal is to optimize backup data throughput
from the clients across the network to the backup tape devices, these tests show that the optimal
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Data Throughput (MB/s)
Number of backup data streams
8 buffs / 64KB
blks
32 buffs / 256KB
blks